This invention relates to a shielded connector for terminating individual conductors, in a shielded manner, of flat ribbon cable. More particularly, the invention relates to a shielded connector for terminating coaxial type individual conductors of a shielded flat ribbon cable whereby shielding of the conductors is maintained even at the termination thereof.
In the prior art various techniques for terminating single conductor coaxial cables of the shielded type are known. More particularly, the techniques and devices are generally employed for terminating typically, coaxial cables of a size rated as 75 ohm cable as well known to those of ordinary skill in the art. These coaxial cables are generally made up of a central copper conductor or other conductor material surrounded by an insulating layer or a layer of dielectric material of cylindrical shape around the central conductor. This layer is in turn surrounded by a shielding cylindrical tubular metallic braid which forms an outer conductor of the coaxial cable. The outer tubular conductor is generally in turn covered with a cylindrical layer of insulation which is made of a material having, in addition to its insulating properties, a good mechanical and weather resistance.
These coaxial cables are typically large enough that they can be easily terminated by simple structures. In preparation to attaching a connector to such a coaxial cable, the cable is first dressed by removing the outer covering for a predetermined distance from the end of the cable. The braided conductor and inner dielectric layer are then cut off at a different predetermined distance to expose the central conductor, and the braided conductor is then folded over the outer layer, and the connector slipped over the entire assembly to establish electrical connection between the outer body of the connector and the braided conductor as well as between the central conductor and an isolated central conductor part of the connector body. The connector is then crimped onto the outside of the cable to hold the braided conductor against the exterior of the cable and thereby effect secure termination and attachment to the end of the cable.
Such typical cable terminating connectors are employed in numerous high frequency radio wave applications at the input of a radio receiver or output of a radio transmitter and/or television antenna applications. As noted these connectors are simple one piece connectors and are well known to those of ordinary skill in the art.
In other applications which require secure shielding and connection to a like connector or device, such as for example, computer applications and/or oscilloscope-type applications, a different type of connector is employed which involves a slot-type engagement mechanism whereby the engagement mechanism of the connector is spring loaded to effect secure connection. The connecting operation typically provides that an engagement portion is rotated in the coupling of slots of the connector with projections of the connector to which it is to be connected. These connectors are also well known in the art and are used extensively to terminate the above-discussed coaxial cables in specialty applications.
Other variations in coaxial cable shielded-type connectors are disclosed in U.S. Pat. Nos. 3,488,625, 3,697,930 and 4,243,290. The environment in which all of these connectors are employed is in use with relatively large coaxial cables such as the 75 ohm cables discussed above. It is relatively easy with said connectors to terminate such cables due to the fact that the metallic braid is relatively large and can be easily folded over the external sheath of the cable and thereby attached to the outer shield of the connector.
On the other hand, in more recent times, it has been found that in the environment of computer communications wherein flat multi-conductor cables are employed, radio frequency interference is often a problem. Typically in the past the flat multi-conductor cables have not employed shielded coaxial-type individual conductors and thus, the use of the shielded terminating connector was never contemplated since to employ it would be to no avail since the cable conductors themselves were not shielded throughout the length thereof and thus, subject to significant RF interference. An example of this is found in office environments wherein typically cable lengths between individual computers and/or peripheral devices were limited to no more than about 50 feet due to the extensive interference caused by high noise office environments, and which typically resulted in disruption of computer communications.
In recognition of the problem, in more recent times, there has been developed a flat ribbon cable employing coaxial-type shielded individual conductors. One example of such a flat ribbon cable coaxial assembly is disclosed in U.S. Pat. No. 3,775,552 to Schumacher. In such flat ribbon cable assemblies, each conductor section of the flat ribbon cable is generally separable as an entity from the remainder of the flat ribbon cable. Once separated, the conductor sections will, as in the case with the 75 ohm-type larger size conductors, include a central conductor such as a copper wire. This copper wire is surrounded by a jacket of cylindrical shape which is made of insulating material and/or dielectric material. The dielectric is typically polytetrafluoroethylene, commonly available under the trademark Teflon.RTM. from Dupont Corporation. This dielectric is then wrapped with a thin braid of aluminized mylar employed for shielding, and having a drain wire in contact therewith which is a single strand of wire running parallel to the center conductor and in conjunction with the aluminized mylar wrap. The outer jacket is then also of insulating material, and is weather resistant, and when forming part of the ribbon cable is attached to other like outer jackets of similar conductors as will be readily apparent to those of ordinary skill in the art.
Although providing individually shielded conductors for a flat ribbon cable, due to the relatively smaller size of such conductors as compared to typical 75 ohm conductors, it becomes difficult to terminate the individual conductors and still maintain effective shielding for the cable assembly. More particularly, in dressing the end of the conductor, the mylar, due to it being a very thin layer, cannot be terminated properly to permit folding over and thus, one has to rely on the drain wire to provide the conductive path to the terminating connector to complete the shielding. However, there has been no readily apparent way to insure secure attachment to such small individual conductors without severing the conductors and/or causing serious defects in the conductor and thus, detrimentally affecting shielding thereof.